Multi-point welding method and catalyst support produced thereby

ABSTRACT

Disclosed is a multi-point welding method capable of certainly welding an object having a number of points to be welded for a short time. First, an approximately cylindrical base body is formed by alternately laminating a flat sheet and a corrugated sheet and then winding them in a spiral shape. In this case, there exist a number of contact points of the flat sheet to the corrugated sheet, that is, points to be welded. Next, there is provided an electrode apart from one end surface of the base body by a specified interval and facing to the end surface. After that, by intermittently applying a current across the electrode and the one end surface of the base body thereby intermittently generating electric discharges between the electrode and the one end surface of the base body, to thus fuse and weld the points to be welded of the flat sheet to the corrugated sheet. With this arrangement, it is possible to certainly weld multi-points to be welded for a short time by only intermittently applying electric discharges.

TECHNICAL FIELD

The present invention relates to a method of welding multi-points to bewelded for a short time and an object produced thereby, for example, acatalyst support for purifying exhaust gas.

BACKGROUND ART

An example of an object having multi-points to be welded includes acatalyst support for purifying exhaust gas. The catalyst support iscomposed of a base body formed by alternately laminating a flat sheetand a corrugated sheet and then winding them in a spiral shape, and anouter shell mounted around the outermost periphery of the base body forfixing the base body and enhancing the strength thereof. In such acatalyst support, the flat sheet needs to be welded to the corrugatedsheet for preventing separation therefrom. However, there exist a numberof contact points of the flat sheet to the corrugated sheet, that is,there exist a number of points to be welded corresponding to the contactpoints.

For joining the flat sheet to the corrugated sheet, there have beenproposed techniques, for example, a brazing method disclosed in JapanesePatent Laid-open No. sho 61-199574 and a laser welding method disclosedin Japanese Patent Laid-open No. sho 63-185627.

Also, there has been proposed a method of joining the outermostperiphery of the base body to the outer shell, for example, a caulkingmethod disclosed in Japanese Patent Publication No. sho 57-55886.

However, the above brazing method disclosed in Japanese Patent Laid-openNo. sho 61-199574 has a disadvantage that the metal made flat sheet orcorrugated sheet is heat-affected in brazing to be deteriorated in itsheat resistance.

Also, the above laser welding method disclosed in Japanese PatentLaid-open No. sho 63-185627 is a difficulty of perfectly joining all ofthe contact points of the flat sheet to the corrugated sheet.Accordingly, for perfect joining of all of the contact points, a laserbeam needs to be scanned over the whole range of the end surface of thebase body, which causes a problem of taking a long time.

Further, the above caulking method for joining the base body to theouter shell, disclosed in Japanese Patent Publication No. sho 61-199574,has a disadvantage that a joining process for the base body and outershell must be separated from a base body forming process, thusincreasing the time required for production.

Taking the above into consideration, an object of the present inventionis to provide a multi-point welding method wherein multi-points to bewelded are certainly welded for a short time. Another object of thepresent invention is to provide a method of producing a catalyst supportfor purifying exhaust gas wherein a flat sheet is certainly welded to acorrugated sheet for a short time thereby obtaining a catalyst supportfor a short time. A further object is to provide a catalyst support forpurifying exhaust gas wherein a flat sheet is certainly welded to acorrugated sheet for a short time.

DISCLOSURE OF THE INVENTION

To achieve the above object, the present inventors have earnestlystudied and noticed the fact that, the electric discharge machining,used in only cutting such as diesinking or wire-cut, functions togenerate a large number of instantaneous electric discharges and henceto fuse the surface of the object thereby performing diesinking orwire-cut, and consequently examined the application of the aboveelectric discharge machining to the joining process Of multi-points.

The present inventors have thus found that the above electric dischargemachining is applicable to electric discharge welding by interruptingelectric discharges existing at a point to be welded before the objectis fused and cut, and therefore, have adopted the above technique as amulti-point welding method.

In a first aspect of the present invention, there is provided amulti-point welding method comprising the steps of: bringing points tobe welded of an electric conductive first object to an electricconductive second object in contact with each other; mounting anelectrode apart from the points to be welded of the first object to thesecond object by a specified interval and facing to at least the pointsto be welded; and intermittently applying a current across the electrodeand at least one of the first and second objects thereby intermittentlygenerating electric discharges at least between the electrode and thepoints to be welded.

In a second aspect of the present invention, there is provided amulti-point welding method adapted to produce a catalyst support forpurifying exhaust gas, comprising the steps of: forming an approximatelycylindrical base body by alternately laminating a metal made flat sheetand a metal made corrugated sheet and then winding them in a spiralshape; mounting an electrode apart from one end surface of the base bodyby a specified interval and facing thereto; and intermittently applyinga current across the electrode and the base body thereby intermittentlygenerating electric discharges in an interval between the electrode andthe one end surface of the base body to thus fuse and join the contactpoints of the flat sheet to the corrugated sheet.

In a third aspect of the present invention, there is provided amulti-point welding method adapted to produce a catalyst support forpurifying exhaust gas, comprising the steps of: forming an approximatelycylindrical base body by alternately laminating an electric conductivemetal made flat sheet and an electric conductive metal made corrugatedsheet having approximately the same shape as the flat sheet and thenwinding them in a spiral shape; mounting an outer shell around theoutermost periphery of the base body; mounting an electrode apart fromone end surface of the base body by a specified interval and facingthereto; and intermittently applying a current across the electrode andthe base body thereby intermittently generating in an interval betweenthe electrode and base body to thus fuse and join the flat sheet,corrugated sheet and outer shell to each other at the same time.

In a fourth aspect of the present invention, there is provided acatalyst support formed by alternately laminating a flat sheet andcorrugated sheet and then winding them in a spiral shape, wherein thecontact points of the flat sheet to the corrugated sheet are fused andwelded to each other by a multi-point welding method of facing anelectrode to one end surface of the catalyst support and intermittentlygenerating electric discharges between the electrode and the one endsurface of the base body.

According to the present invention, the contact points of the firstobject to the second object are subjected to intermittent electricdischarges and are welded.

Specifically, in welding, when electric discharges are temporarily cutoff, a point subjected to electric discharges is in a fused state, andaccordingly, has a discharge distance made longer than that of the otherpoints to be welded. As a result, since electric discharges are liableto be generated at a point having a short discharge distance, the nextelectric discharges never fail to be generated at the other any one ofpoints to be welded. Thus, by intermittently generating electricdischarges, the points to be welded are sequentially welded. Also,electric discharges are not generated at the point welded once, therebypreventing a problem of generating excessive fused loss at the contactpoints. Therefore, it is possible to certainly weld a number of contactpoints of the first object to the second object by only intermittentlygenerating electric discharges.

As mentioned above, the present invention is so constituted that theflat sheet is welded to the corrugated sheet by intermittentlygenerating electric discharges at the end surface of the base bodycomposed of the flat sheet and corrugated sheet which are alternatelylaminated and then wound. Accordingly, by only intermittently generatingelectric discharges on the one end surface of the base body, there canbe realized certain welding between the flat sheet and corrugated sheet.

Also, the present invention achieves not only the joining of the basebody to the outer shell for a short time but also the joining among theflat sheet, corrugated sheet and outer shell at the same time, whichenables production of a catalyst support for purifying exhaust gas for ashort time.

Further, since the present invention is characterized by electricdischarge welding the end surface of a catalyst support composed of aflat sheet and a corrugated sheet alternately laminated and then wound,it is possible to secure high ventilation resistance in comparison withthe case using the conventional brazing method having a possibility thatbrazing filler metal used for bonding the flat sheet to the corrugatedsheet is protruded in a gas passage formed by the flat sheet andcorrugated sheet.

Compared with a laser welding method, in the present invention, electricdischarges are certainly generated at the contact points of the flatsheet to the corrugated sheet, and therefore, there can be obtained acatalyst support composed of the flat sheet and corrugated sheetcertainly welded to each other.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view of a base body;

FIG. 2 is an explanatory view showing a forming process of a firstembodiment;

FIG. 3 is an explanatory view showing a welding process of the firstembodiment;

FIG. 4 is a perspective view of a honeycomb catalyst support;

FIG. 5 is an explanatory view showing a welding process of a secondembodiment;

FIGS. 6a and 6b are views for explaining the second embodiment; and

FIG. 7 is an explanatory view showing a third embodiment.

BEST MODE OF CARRYING OUT THE INVENTION

Referring to FIG. 1, there is shown a base body of a honeycomb catalystsupport for purifying exhaust gas according to the present invention.

A base body is composed of a flat sheet 2 as a first object and acorrugated sheet 3 as a second object. The flat sheet 2 and corrugatedsheet 3 are made of ferritic heat resisting stainlesssteel(75Fe-20Cr-5A1-REM) and have a thickness of 50 μm. In addition, thecorrugated sheet 3 has a pitch of 1.25 mm.

The flat sheet 2 and corrugated sheet 3 are alternately laminated andthen wound, to thus form a cylindrical base body having a diameter ofapproximately 77 mm and an axial length of 105 mm. The base body thusobtained has a number of ventilation holes formed by the flat sheet 2and corrugated sheet 3.

As shown in FIG. 2, in a base body forming process for forming acylindrical base body 1 by winding the flat sheet 2 and corrugated sheet3, the flat sheet 2 is brought in contact with the corrugated sheet 3 ata number of vertexes of the corrugated sheet 3.

FIG. 3 is an explanatory view showing an electrode mounting process anda joining process wherein the flat sheet 2 is welded to the corrugatedsheet 3.

First, in the electrode mounting process, there is prepared an electricdischarge machine 10 (ED-28®, Makino Seisaku) capable of intermittentlygenerating electric discharges by intermittently applying a current. Theelectric discharge machine 10 has a first copper made electrode plate 11having a size of 100 mm×100 mm×20 mm, and a second electrode 14 which ismounted on the bottom portion 13a of a vessel 13 filled with a workingliquid 12 at such a position as facing to the first electrode 11. Withthis arrangement, a current is applied across the first and secondelectrodes 11 and 14, to intermittently generate electric discharges.

The working liquid 12 serves to eliminate fused substances generated byelectric discharge welding and to prevent temperature rise of theworkpiece. Further, with the aid of the working liquid 12, the electricdischarges are intermittently generated by the intermittently appliedcurrent in the electric discharge machine 10 is allowed toinstantaneously disappear at the time of cutting off a current.

Between the first and second electrodes 11 and 14, there are provided apower supply 15 for supplying a voltage and a current control unit 16for controlling a current.

Subsequently, the cylindrical base body 1 obtained in the base bodyforming process is brought in electric contact at one end surface lathereof with the second electrode 14 of the electric discharge machine10, and is dipped in the working liquid 12. In this case, as the workingliquid 12, there is used a Titan cleaner No. 6A mainly containingkerosene.

Next, in a welding process, a power supply 15 applies a voltage ofapproximately 60 V across the electrode 11 and the second electrode 14,after which the electrode 11 is moved closely to the other end surface1b of the base body 1 thus starting electric discharging between the endsurface 1b of the base body 1 and the electrode 11. In the above, theapplied current is controlled to be 24A. Further, the aforesaid currentcontrol unit 16 intermittently switches the current flow to therebyintermittently generate electric discharges in the range of a pulsewidth of 200 millisecond (ms).

Consequently, electric discharges are generated at the contact points ofthe flat sheet 2 to the corrugated sheet 3.

The contact points thus subjected to electric discharges are fused andwelded to each other, and has the discharge distance between the firstelectrode 11 and the same made longer by the fused width caused by theelectric discharges. Since electric discharges are liable to begenerated at the point having a short discharge distance, the nextelectric discharges are generated not at the portion subjected toelectric discharges once but at the other any one of contact points ofthe flat sheet 2 to the corrugated sheet 3. Therefore, it is possible toweld for a short time the several thousands of contact points of theflat sheet 2 to the corrugated sheet 3 existing along the end surface 1bof the base body 1.

Further, for enhancing the strength of the base body 1 itself, in thisembodiment, the flat sheet 2 and the corrugated sheet 3 are welded toeach other at the opposed end surface 1a of the base body 1 in the samemanner as mentioned above.

As for welding of the flat sheet to the corrugated sheet, the presentinvention will be compared with the conventional blazing method andlaser welding method.

The blazing method has a disadvantage of giving a great deal of heat tothe flat sheet and the corrugated sheet thus deteriorating heatresistance of the base body.

In the laser welding method, for perfect welding of the flat sheet tocorrugated sheet along the end surface of a base body having a diameterof 86 cm, it needs the welding speed at a pitch 0.5 mm, which takesapproximately 30 min.

Conversely, the electric discharge welding of the present inventionmakes it possible to perfectly weld the flat sheet to the corrugatedsheet of the base body identical to the above for a short time, such as3 min.

Hereinafter, there will be described a method of producing a honeycombcatalyst support wherein the flat sheet 2 is joined to the corrugatedsheet 3 and the base body 1 composed of the flat sheet 2 and corrugatedsheet 3 is joined to the outer shell 20.

FIG. 4 shows a honeycomb catalyst support including a base body 1composed of the flat sheet 2 and corrugated sheet 3 alternatelylaminated and then wound, and an outer shell 20 mounted around theoutermost periphery of the base body 1 for fixing the base body portionand enhancing the strength thereof.

With reference to FIG. 5, there will be explained a method of producingthe honeycomb catalyst support according to a second embodiment.

First, in a base body forming process, there is obtained a base body 1composed of a flat sheet 2 and corrugated sheet 3 (not joined to eachother yet) having an axial length of 105.2 mm and a diameter of 77 mm.

After that, around the outermost periphery of the base body 1, there ismounted an outer shell having a thickness of approximately 1.5 mm(larger than that of the flat sheet), axial length of 105 mm, innerdiameter of 77 mm and outer diameter of 80 mm. In this case, the basebody 1 is protruded at both the ends thereof from the outer shell byapproximately 0.1 mm.

Next, in an electrode mounting process, likely to the first embodiment,one end surface of a honeycomb catalyst support 21 (not welded yet) ismounted on a second electrode 14 of the electric discharge machine 10 insuch a manner as to be electrically conducted. Also, a first electrode11 is mounted so as to face to the other end surface of the base body 1.

After that, in a joining process, a power supply 15 applies a voltage of60 V (20-30A) across the electrode 11 and the second electrode 14, and acurrent control unit 16 operates to intermittently generate electricdischarges within the range of a pulse width of 200 ms, thus welding theother end surface of the honeycomb catalyst support 21.

FIG. 6 is a view for explaining the reason why the base body 1 isprotruded at both the ends thereof from the outer shell by approximately0.1 mm.

The honeycomb catalyst support prior to electric discharge welding isformed such that the end surface of the base body 1 is protruded fromthe end surface of the outer shell 21 as shown in FIG. 6a. This is whythe thickness (approximately 0.05 mm) of the flat sheet 2 and corrugatedsheet 3 constituting the base body 1 is extremely smaller than thethickness (approximately 1.5 mm) of the outer shell 20, and accordingly,the end surface of the base body 1 is fused by electric dischargewelding more rapidly than the outer shell 20.

FIG. 6b is a typical view showing a honeycomb catalyst support afterelectric discharge welding. As shown in this figure, by protruding theend surface of the base body 1 from the outer shell 21, it is possibleto line up the end surface of the base body 1 with that of the outershell 21 after termination of the electric discharge welding.

In the embodiments mentioned above, the base body is formed in acylindrical shape; however the form thereof is not limited thereto butmay be an elliptic shape in cross-section.

FIG. 7 is a view for explaining a third embodiment of the presentinvention.

In the embodiments mentioned above, a current is intermittently appliedto intermittently generate electric discharges. However, in thisembodiment, using the nature of the electric discharge being liable tobe generated at the point having a short discharge distance, theelectrode is formed with irregularity on the surface facing to thepoints to be welded as shown in FIG. 7.

In generation of electric discharges between the base body 1 and theelectrode 30, the electrode 30 is rotated around the axis of the basebody 1. This rotation changes the discharge distance between theelectrode 30 and the base body 1 thus intermittently generating electricdischarges, which makes it possible to weld a number of points to bewelded.

The condition of the electric discharge welding is not limited to theembodiments mentioned above but may be freely selected in voltage,current and welding time within the range of certainly welding the flatsheet to the corrugated sheet and obtaining the desired shape.

In the embodiment mentioned above, by protruding the base body from theouter shell, it is possible to line up the end surface of the base bodywith that of the outer shell after termination of electric dischargewelding. However, there may be proposed a modification of making the endportion of the outer shell on the electric discharge welding side into atapered shape, whereby the thickness of the outer shell at the taperedend portion is made similar to that of the flat sheet and corrugatedsheet thus obtaining the same effect as mentioned above.

As mentioned above, the present invention is adapted for a catalystsupport for purifying exhaust gas. However, it is not limited to themethod of producing the catalyst support but may be adapted to anyapplication necessary for certainly welding an object having a number ofpoints to be welded for a short time.

In the embodiment mentioned above, the electrode is rotated around theaxis of the base body; however it may be moved so as to change thedischarge distance between the base body and the electrode facingthereto thus intermittently generating electric discharges.

Further, in the embodiment mentioned above, electric discharges aregenerated only one time at one point to be welded; however, the presentinvention is not limited to the above. If a plurality of points can bewelded, electric discharges may be generated plural times at one pointto be welded.

INDUSTRIAL APPLICABILITY

As described in detail, the present invention is effective for weldingmulti-points to be welded for a short time, for example, for welding aflat sheet to a corrugated sheet of a catalyst support for purifyingexhaust gas.

We claim:
 1. A multi-point welding method comprising the stepsof:bringing points to be welded of an electric conductive first objectand points of an electric conductive second object in contact with eachother; mounting an electrode apart from said points to be welded of saidfirst object by a specified interval so that the electrode and the firstobject are in a non-contacting state and said electrode faces at leastsaid point to be welded of said first object; and intermittentlyallowing a current to flow between said electrode and either of saidfirst object and said second object neither of which contact saidelectrode, thereby intermittently generating electric discharges atleast between said electrode and said points to be welded; wherein saidfirst object, said second object and said electrode are dipped in aliquid for preventing heat caused by electric discharges between saidelectrode and said points to be welded.
 2. A multi-point welding methodaccording to claim 1, wherein said electrode is movable so as to changesaid specified interval.
 3. A multi-point welding method comprising thesteps of:forming an approximately cylindrical base body by alternatelylaminating a metal made of a flat sheet and a corrugated sheet and thenwinding said flat sheet and said corrugated sheet in a spiral shape;mounting an electrode apart from one end surface of said base body by aspecified interval so that said electrode does not contact said basebody and said electrode faces to said one end surface; andintermittently allowing a current to flow between said electrode andsaid base body thereby intermittently generating electric dischargesbetween said electrode and said one end surface of said base body, tothus fuse and weld contact points of said flat sheet to said corrugatedsheet.
 4. A multi-point welding method according to claim 3, whereinsaid electrode and said base body are dipped in a working liquid forpreventing excessive heating caused by electric discharges generatedbetween said electrode and said base body.
 5. A multi-point weldingmethod according to claim 3, wherein said electrode is formed with oneof a protrusion and a cavity on the surface facing said one end surfaceof said base body and said electrode is rotated around the axis of saidbase body in said electric discharge welding process.
 6. A multi-pointwelding method according to claim 3, said flat sheet and said corrugatedsheet are formed having a rectangular shape and are wound in a spiralshape such that the short side of said rectangular shape is taken as theaxial length of said base body.
 7. A multi-point welding methodcomprising the steps of:forming an approximately cylindrical base bodyby alternately laminating an electric conductive metal made of a flatsheet and an electric conductive metal made of a corrugated sheet havingapproximately the same shape as that of said flat sheet, and winding theflat sheet and the corrugated sheet in a spiral shape; forming an outershell around an outermost periphery of said base body; mounting anelectrode apart from one end surface of said base body by a specifiedinterval so that said electrode does not contact said base body and saidelectrode faces said end surface; and intermittently allowing a currentto flow between said electrode and said base body thereby generatingelectric discharges in said interval, to thus fuse and weld said flatsheet, said corrugated sheet and said outer shell to each other at thesame time.
 8. A multi-point welding method according to claim 7, whereinsaid outer shell is mounted around the outermost periphery of said basebody such that said base body is protruded from said outer shell by atleast a reduced width of said flat sheet and said corrugated sheetthrough electric discharge welding.
 9. A catalyst support composed of aflat sheet and a corrugated sheet alternately laminated and then wound,wherein contact points of said flat sheet to said corrugated sheet arefused and welded to each other by a multi-point electric dischargewelding method including mounting an electrode facing one end surface ofsaid catalyst support with a specific interval therebetween so that saidcatalyst support and said electrode do not contact one another andintermittently generating electric discharges between said electrode andsaid one end surface of said catalyst support.
 10. A catalyst supportaccording to claim 9, wherein at least said catalyst support is dippedin a working liquid.